In the modern manufacturing process used for making various types of light bulbs, a high-speed ribbon machine is used. The glass ribbon machine takes a thin, molten strip of glass and presses out bulbs at the rate of up to 2000 bulbs per minute or more. The key features of the machine are: a glass ribbon, a metal tip through which air is blown, an orifice plate that the glass ribbon rides upon and conveys the bulbs, and a quench mold or rotating split mold that cools the bulb to the desired shape and dimensions. The process is such that a molten ribbon of glass rides on top of a chain of steel plates, wherein each plate contains an orifice that is the size of the open end of the bulb. As the glass ribbon rides on the chain of plates, a tip presses the glass ribbon into the orifice and blows air to force the glass to drop through the orifice into a tear-drop shape. As soon as the bulb is the desired size, a pair of molds that have been soaked in water, will cover the bulb without touching it. The heat of the molten glass instantly turns the water to steam, and the steam quenches the glass to its final form. A push rod then ejects the bulb from the orifice plate, and the bulb falls onto a conveyor belt for further processing.
The primary area or component of wear on the ribbon machine and similar types of high-speed bulb making machines is the quench mold. Although there is typically no significant direct contact between the glass and the inner surface of the mold, the combination of hot steam and heat work to degrade the surface texture of the mold. The degradation is often so severe that the bulbs must be changed every 2 to 5 days of continuous operation. This causes considerable amounts of downtime and cost.
Significant amounts of time and labor are used for applying a sacrificial coating to the quench molds. As depicted in FIG. 1A, a mold section 10 may include a housing 11 and an interior cavity section 12. The interior sections may include one or more vents 13 and a coating to both retain moisture and reduce adhesion of the glass to the mold cavity. This coating may be made by painting a resin, such as linseed oil, onto the bare steel surface of the inside of a mold. While the oil is still wet, a tightly sized cork dust may be sprinkled onto the oil layer. This oil is then allowed to air dry, after which the excess cork is tapped off of the coating. The molds are placed into an oven and baked for 3 to 4 hours at 400° F. The resulting coating is a very rough and highly convoluted texture with a high surface area that is good for holding or retaining water. When measured using a Hommel surface profilometer, the surface roughness (Ra) may be about 40 microns. In addition, the surface may have a peak-to-valley height (Rmax) of about 250 microns and a mean peak-to-valley distance of about 200 microns. FIGS. 1B and 1C depict photomicrographs of this prior art coating on a bulb quench mold at 15× and 150× magnification, respectively.
Although the prior art cork coatings work well, such coatings typically last for only about 2 to 5 days in continuous production on a ribbon machine. On a large machine, there may be as many as 200 mold sets that must be changed out at one time. The downtime to replace these parts is often 1 to 2 hours, resulting in a loss of production of 12,000 to 24,000 bulbs, plus the cost of the coatings.
The disclosure contained herein is directed to solving at least some of the problems described above.